1. Field of the Invention
The present disclosure relates to a belt drive device that restricts, with respect to an endless belt laid under tension across a drive roller and a driven roller, meandering of the belt in an axis direction of the rollers (roller axis direction), a fixing device provided with the same, and an image forming apparatus.
2. Description of the Related Art
Conventionally, in an image forming apparatus, a toner image formed on an image bearing member such as a photosensitive member is transferred onto a recording medium, and the recording medium carrying the toner image is conveyed toward a fixing device, where heat and pressure are applied thereto so that the toner image on the recording medium is fixed onto the recording medium. As the fixing device, there is a belt fixing type fixing device including a fixing belt that is rotatably laid under tension across a fixing roller and a heat roller and a pressing roller that is placed in press contact with the fixing belt, in which a toner image is fixed onto a recording medium while being passed through a nip portion between the fixing belt and the pressing roller.
In the belt fixing type fixing device, when the fixing belt laid under tension across the rollers are being rotated, the fixing belt may move to meander on the rollers in a roller axis direction. Such meandering of the fixing belt is problematic in that it leads to a fixing failure such as a toner image being positionally displaced on a recording medium, and continued meandering of the fixing belt might cause a breakage of end portions of the belt in a width direction thereof, which has been disadvantageous. Furthermore, not only in the belt fixing type fixing device but also with an endless belt laid under tension over a plurality of rollers including a drive roller, such as, for example, an intermediate transfer belt onto which a toner image is transferred or a conveyer belt for carrying and conveying a recording medium, there occurs a problem similar to the above.
In order to avoid this, there is conventionally known a technique for suppressing belt meandering. For example, in a belt drive device described in Patent Document 1, there is provided a press contact member that comes into press contact with a belt on one end side thereof in a width direction, which is laid over a drive roller and a driven roller, and a relative positional relationship between the drive roller and the driven roller is adjusted beforehand so as to cause the belt to move to the one end side. When rotating, a belt 12 gradually moves to the one end side, and as the belt moves further to the one end side, one end portion of the belt is pressed against the press contact member. As the one end portion of the belt is pressed further against the press contact member, a force acting to cause the belt to move to the other end side gradually increases to such an extent that the forces acting to cause the belt to move to the both end sides, respectively, become balanced. When these forces acting to cause the belt to move to the both end sides become balanced, the movement of the belt in the width direction stops, and thus meandering of the belt is restricted.
Furthermore, in a belt drive device described in Patent Document 2, at one end portion of a belt, a rib annularly protruding along a running direction of the belt and a restriction member that is contactable with the rib are provided, and when the belt meanders, the rib provided at the belt comes into contact with the restriction member, thus restricting meandering of the belt.
Furthermore, a belt drive device described in Patent Document 3 includes a belt that is laid under tension over a drive roller and a meandering correction roller, a meandering detection sensor that comes into contact with an end portion of the belt and detects meandering of the belt, a meandering correction cam that is driven to rotate by a motor so as to cause the meandering correction roller to swing, and a clutch that causes the motor to rotate based on a result of detection by the meandering detection sensor. Upon the meandering detection sensor detecting meandering of the belt, the clutch becomes engaged to transmit a rotary force of the motor to the meandering correction cam. This causes the meandering correction cam to start rotating, so that the meandering correction roller swings in such a direction as to correct the meandering of the belt.